1. Field of the Invention
The invention relates to fasteners, and more particularly to fasteners for tacking (e.g. temporarily holding) two or more parts together.
2. Background Information
In many environments, it is necessary to temporarily hold and clamp parts together while other operations, such as drilling and riveting, are performed. For example, tack fasteners are widely used in the aircraft industry to temporarily attach the sheets of metal used to form the skin of an aircraft to the flanges of supporting structural elements, such as stringers and frames. Since it is time consuming and sometimes difficult (and therefore expensive) to temporarily fasten parts together using conventional mechanical devices, such as nuts and bolts, tack fasteners have been developed to avoid these problems. While various tack fasteners have been developed, those that require access to only one side of the parts to be fastened together are preferred, at least in the aircraft industry.
In addition to being undesirably complex, one disadvantage of the prior art tack fasteners, particularly those used in the aircraft industry, resides mainly in the inability to provide the high compression forces that are occasionally needed to pull parts together. In the past, this disadvantage has been overcome by utilizing nuts and bolts in regions where abnormally high compression forces are required and/or using a large number of closely spaced tack fasteners. Obviously, both approaches have disadvantages. The installation of nuts and bolts is time consuming and frequently requires the services of two employees, rather than a single employee. The use of large numbers of tack fasteners requires the creation of additional tack fastener holes, which is undesirable.
In general, the primary disadvantage of current tack fasteners is their inability to supply high compression forces while at the same time providing hole concentricity alignment, along with quick set-up and removal. While some tack fasteners provide one or two of these features, none provide all four.
The most commonly used temporary one-sided fasteners don't provide the required concentricity alignment for high tolerance holes, as well as the high clamp-up forces that are commonly required. These one-sided fasteners have parallel tangs that project and expand outwardly in only one axis, which can allow slippage 90.degree. from that axis. In addition, the installation of these fasteners often requires two hands to prevent the rotation of the tangs with respect to the hole, until the fastener parts are drawn together with enough force to hold the tangs. Additionally, some fasteners will stick in the hole during removal, and may also damage the surrounding structure of the hole as a result of the high clamp-up forces.